Dead cells compactly arranged with suberin in their walls.
Explanation
As the stems of dicotyledonous plants undergo secondary growth and increase in girth, the outer epidermal layer is ruptured and replaced by a protective tissue called the periderm. The outer layer of the periderm consists of cork cells (phellem).- Living cells with large intercellular spaces for gas exchange. is Incorrect: Cork cells are not living at maturity. Living cells with large intercellular spaces typically describe parenchyma tissue, which is involved in storage and photosynthesis, not the protective function of cork.
- Dead cells compactly arranged with suberin in their walls. is Correct: Cork cells are dead at maturity and are compactly arranged without intercellular spaces. Their cell walls are heavily thickened with a waxy substance called suberin. This suberin deposition makes the cells impervious to water and gases, providing effective protection against water loss, mechanical injury, and microbial infection.
- Meristematic cells that actively divide to form new bark. is Incorrect: Cork cells are differentiated permanent tissues, meaning they have lost the ability to divide. The meristematic tissue responsible for producing cork cells is the cork cambium (phellogen), not the cork cells themselves.
- Epidermal cells containing stomata for transpiration. is Incorrect: Cork cells replace the original epidermal cells. While the epidermis contains stomata, the cork layer is continuous and impervious. Gas exchange in older stems occurs through lens-shaped openings in the bark called lenticels, not through stomata within the cork cells.
Key Takeaway: Cork cells are characterized by being dead at maturity, lacking intercellular spaces, and possessing suberized walls that make them impermeable to water and gases.